.

wcfs/zblk.go

+// Copyright (c) 2001, 2002 Zope Foundation and Contributors.
+// All Rights Reserved.
+//
+// This software is subject to the provisions of the Zope Public License,
+// Version 2.1 (ZPL).  A copy of the ZPL should accompany this distribution.
+// THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED
+// WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+// WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS
+// FOR A PARTICULAR PURPOSE
+//
+// XXX clarify on licensing (ZPL for BTrees)
+//
 // Copyright (C) 2018  Nexedi SA and Contributors.
 //                     Kirill Smelkov <kirr@nexedi.com>
 //
@@ -34,7 +46,7 @@ import (
 
 // XXX start from loading ZBigFile btree
 
-
+// ZBigFile mimics ZBigFile from python.
 type ZBigFile struct {
 	pyobj *zodb.PyObject
 
@@ -86,3 +98,148 @@ func (conn *zpyconn) loadZBigFile(ctx context.Context, oid zodb.Oid) (*ZBigFile,
 
 	// XXX ok
 }
+
+
+
+// ZBucket mimics ?OBucket from btree/py, with ? being any integer.
+//
+// py description:
+//
+// A Bucket wraps contiguous vectors of keys and values.  Keys are unique,
+// and stored in sorted order.  The 'values' pointer may be NULL if the
+// Bucket is used to implement a set.  Buckets serving as leafs of BTrees
+// are chained together via 'next', so that the entire BTree contents
+// can be traversed in sorted order quickly and easily.
+type ZBucket struct {
+	pyobj *zodb.PyObject
+
+	next   *ZBucket		// the bucket with the next-larger keys
+	keys   []KEY		// 'len' keys, in increasing order
+	values []interface{}	// 'len' corresponding values		XXX merge k/v ?
+}
+
+// zBTreeItem mimics BTreeItem from btree/py.
+type zBTreeItem {
+	key	KEY
+	child	interface{}	// ZBTree or ZBucket
+}
+
+// ZBTree mimics ?OBTree from btree/py, with ? being any integer.
+//
+// See https://github.com/zopefoundation/BTrees/blob/4.5.0-1-gc8bf24e/BTrees/Development.txt#L198
+// for details.
+type ZBTree struct {
+	pyobj *zodb.PyObject
+
+	// firstbucket points to the bucket containing the smallest key in
+	// the BTree.  This is found by traversing leftmost child pointers
+	// (data[0].child) until reaching a Bucket.
+	firstbucket *ZBucket
+
+	// The BTree points to 'len' children, via the "child" fields of the data
+	// array.  There are len-1 keys in the 'key' fields, stored in increasing
+	// order.  data[0].key is unused.  For i in 0 .. len-1, all keys reachable
+	// from data[i].child are >= data[i].key and < data[i+1].key, at the
+	// endpoints pretending that data[0].key is minus infinity and
+	// data[len].key is positive infinity.
+	data	[]zBTreeItem
+}
+
+// Get searches BTree by key.
+//
+// It loads intermediate BTree nodes from database on demand as needed.
+// XXX ok -> ErrKeyNotFound?
+func (t *ZBTree) Get(ctx context.Context, key KEY) (interface{}, bool, error) {
+	t.PActivate(ctx)	// XXX err
+
+	if len(t.data) == 0 {
+		// empty btree
+		return nil, false, nil
+	}
+
+	for {
+		// search i: K(i) ≤ k < K(i+1)	; K(0) = -∞, K(len) = +∞
+		i := sort.Search(len(t.data), func(i int) bool {
+			j := i + 1
+			if j == len(t.data) {
+				return true	// [len].key = +∞
+			}
+			return key < t.data[j].key
+		})
+
+		switch child := t.data[i].child.(type) {
+		case *ZBTree:
+			// XXX t.PAllowDeactivate
+			t = child
+			t.PActivate(ctx)	// XXX err
+
+		case *ZBucket:
+			child.PActivate(ctx)	// XXX err
+			return child.Get(key), nil
+		}
+	}
+}
+
+// get searches Bucket by key.
+//
+// no loading from database is done. The bucket must be already activated.
+func (b *ZBucket) get(key KEY) (interface{}, bool) {
+	// XXX b.PActivate ?	XXX better caller? (or inside if get -> Get)
+
+	// search i: K(i-1) < k ≤ K(i)		; K(-1) = -∞, K(len) = +∞
+	i := sort.Search(len(b.keys), func(i int) bool {
+		return key <= t.data[i].key
+	})
+
+	if i == len(b.keys) || b.keys[i] != key {
+		return nil, false // not found
+	}
+	return b.values[i], true
+}
+
+
+// from https://github.com/zopefoundation/BTrees/blob/4.5.0-1-gc8bf24e/BTrees/BTreeTemplate.c#L1087:
+//
+// For an empty BTree (self->len == 0), None.
+//
+// For a BTree with one child (self->len == 1), and that child is a bucket,
+// and that bucket has a NULL oid, a one-tuple containing a one-tuple
+// containing the bucket's state:
+//
+//     (
+//         (
+//              child[0].__getstate__(),
+//         ),
+//     )
+//
+// Else a two-tuple.  The first element is a tuple interleaving the BTree's
+// keys and direct children, of size 2*self->len - 1 (key[0] is unused and
+// is not saved).  The second element is the firstbucket:
+//
+//     (
+//          (child[0], key[1], child[1], key[2], child[2], ...,
+//                                       key[len-1], child[len-1]),
+//          self->firstbucket
+//     )
+//
+// In the above, key[i] means self->data[i].key, and similarly for child[i].
+
+
+// XXX ZBTree.Get(key)
+
+// XXX ZBucket.MinKey ?
+// XXX ZBucket.MaxKey ?
+
+
+// from https://github.com/zopefoundation/BTrees/blob/4.5.0-1-gc8bf24e/BTrees/BucketTemplate.c#L1195:
+//
+// For a mapping bucket (self->values is not NULL), a one-tuple or two-tuple.
+// The first element is a tuple interleaving keys and values, of length
+// 2 * self->len.  The second element is the next bucket, present iff next is
+// non-NULL:
+//
+//	(
+//	     (keys[0], values[0], keys[1], values[1], ...,
+//	                          keys[len-1], values[len-1]),
+//	     <self->next iff non-NULL>
+//	)